The present invention relates generally to an optical pickup device. More particularly, the invention relates to an optical pickup device for performing recording and/or reproduction of information to an optical disk such as, for example, a magneto-optical disk, a phase-changeable optical disk or the like.
Generally, an optical recording/reproducing apparatus having an optical pickup device for an optical disk as a recording medium has an advantage in that an extremely large amount of information can be stored in the optical disk with a high-speed access in comparison to a magnetic recording/reproducing apparatus using magnetic tapes or magnetic disks as a recording medium.
In conventional optical pickup devices used in the above-mentioned optical recording/reproducing apparatus, generally, a light beam emitted from a light source is converted to a parallel light beam and then converged to a recording surface of an optical disk through various optical elements. A light beam reflected by the recording surface of the optical disk is then received by light detecting elements such as photodiodes and converted thereby to an electric signal from which information data can be read. Further, based on the detection of the light beam reflected from the recording surface of the optical disk, servo controls for focusing and tracking of the light beam with respect to the optical disk are performed.
Recently, even in such optical pickup devices, it has been desirable to speed up the accessing operation. In view of this requirement, there has been developed an optical pickup device of a separation type in which an optical system is separated into a stationary optical system and a movable optical system. The stationary optical system is adapted to transmit a light beam emitted from a light source along an incident optical axis thereof which is parallel to a radial direction of the optical disk.
The movable optical system of the conventional optical pickup device comprises a carriage which is movably guided with a guide rail for linear movement in a seeking direction along the incident optical axis of the stationary optical system. The carriage is provided with a deflecting member which has a deflecting face for receiving the light beam transmitted from the stationary optical system along the incident optical axis and for deflecting the same toward the recording surface of the optical disk. The carriage is also provided with an objective lens for converging the light beam deflected by the deflecting member on the recording surface of the optical disk and for leading a light beam reflected by the recording surface of the optical disk toward the deflecting member.
Further, the stationary optical system is provided with a focusing detector and a tracking detector. The light beam reflected by the recording surface of the optical disk is divided into two beam branches after being deflected by the deflecting member so that the beam branches are led to the focusing detector and the tracking detector, respectively.
This construction of the separation-type optical pickup device makes it possible to decrease the number of optical elements to be mounted on the carriage and thereby to reduce the weight and size of the movable optical system.
In the separation-type optical pickup device, however, it is difficult to assemble the carriage with the guide rail with no play therebetween, given the realities of manufacturing tolerances. In this situation, when the carriage is moved in the seeking direction, the play between the carriage and the guide rail causes the carriage to be inclined about an axis which is parallel to the recording surface of the optical disk and perpendicular to the seeking direction. As the carriage is inclined, the deflecting member and the objective lens are also angularly displaced. Accordingly, the inclination of the carriage causes the movable optical system to generate an undesirable offset of the light beam reflected from the optical disk with respect to the incident optical axis of the stationary optical system. Generally, the detection of the tracking condition has to be effected with a tolerance of about 0.03 .mu.m, while the detection of the focusing condition has to be effected with a tolerance of about 0.3 .mu.m.
Accordingly, an occurrence of offset of the reflected light beam with respect to the incident optical axis can greatly influence the detection of tracking condition of the optical pickup device.